I have been chasing this problem for a year now. Its a BG mighty demon 650. It would flood at idle randomly. Well i tore into it and found some debris in the primary bowl (the one giving me problems) so i thought that was it. PUt it back together and it was fine for a little until a few days later, bang did it again. So i shelved it and put on the ebock. that was last fall. Now that i got the headers on the truck i would like to run the better carb. Been tinkering with it, tore it all down again and cleaned it, got the idle tuned in as best as i newbie like me can and thought WOW i got it. Well about 2-3 days later of playing with it in the garage. My eyes started to burn, I had first thought it was my tuning, so i tinkered with it thinking that maybe it was a little to rich. Well after tinkering and not making any diff, i realized maybe i should check the float levels. Primary was over the sight glass.

Tore it apart again and found nothing, put back together and retuned the whole time being fine. Then it did it again, thought it was maybe from the fuel being hot and creating more pressure and blowing passed the needle as i could see bubbles in the filter after shutdown when hot.

Just went out after a few days away from it for a break and started it cold, less than 30 seconds after i got it to idle on its own. Both sight glasses were maxed out, so i reved it a few times to pump the ACC. pumps and the level dropped, as soon as i stoped it went right back up. So i shut it down and within a min. of shut down the fuel pressure guage dropped to 0. It is running right at 7psi while its running so i don't think its to much pressure.

THe floats were set at the proper level when it was fine for the first few times i had it running.

So just thinking that the needle and seats need replaced? Mainly because it doesn't hold pressure after shutdown for any lenght of time.

I'm learning this carb stuff, so I appologize for the newbie post.

 

It sounds like your float is either cracked or defective and is filling up with gas internally. If this happens you'll never cut down on the gas flow.
Needle seats can alo be a problem with trash although trash should be filtered at the carb but I've still experienced issues with trash / needle seats..

 

Thanks for the help, I never really thought about looking at the floats. I'll have to sit them in a cup of gas for a few days and see if they feel heavier. I think they are the foam kind? I should be able to put weight on top of them to completle submerge it in gas and it should not absorb any gas right?

Since i'm going to tear it apart again to check the floats i may just buy new needle and seats for it.

 

try this if floats check out ok
take bowls off carb and adjust floats with bowl upside down .
you want to have the floats way to high (low gas level)
reinstall bowls and start car , now adjust the floats a little at a time till you get them correct . (just dripping on shake)

 

Will do. I'm running out of things to try. For a while It was the primary only, now its both primary and sec. I want to toss a fuel regulator on it when i get a chance before i tear down the carb again. Maybe its just a little more pressure than it can handle, but that doesn't really explain why its bleeding pressure down as soon as its shut off

It will be a day or 2 until i get a chance to pull the carb and check it out. I'll try to post back with what i find.

 

My stock holley had the same intermittant problem and it was the secondary float. The floats were only 3 years old with only about 1500 miles on them.

 

Well this is the first time the secondary started to act up. It has always been the primary up until last week.

I will deff. check them when i pull it apart. Is aggervating, its an awesome carb and i have it set up the way i want and it keeps acting up. lol

 

Sounds like a good way to adjust the floats..

Can’t help but think about what you originally mentioned in the beginning - about finding trash / debris in the primary bowl. Once trash always trash so to speak until you completely purge from the fuel system. You may end up with trash between the needles and seats; assuming the floats are not the problem, this trash issue will continue to plague you until you do a wholesale cleaning of the fuel system..

The final step for remediation of this issue may be : ( not knowing what components have already been replaced on your car) pull the gas tank, clean thoroughly or replace depending on condition, blow out or replace the entire fuel line, new fuel pump and install a fuel filter in the engine bay ahead of the fuel pump for good measure.. Then… you may still have to have the carb rebuilt or cleaned to rid yourself of the issue..

Years back I had a good friend rebuild my Holley 735cfm off of my 428 Mustang. It ran fantastic for while until I discovered trash in the fuel system and it created issues for my carb.. Couldn’t get rid of it.. I wasn’t very happy about this situation so I re-did everything. I pulled the original Holley 735 cfm carb, date coded gas tank ( both put in storage) replaced with a brand new clean gas tank, brand new gas line from tank to engine, rebuilt the fuel pump ( The FE Carter High performance fuel pumps are re-buildable), installed an external fuel filter in the lower part of the engine bay "before the fuel pump" and put a new 750 Holley on top. Before connecting the gas line to the carb, I purged it or cycled gas through the fuel line into a can to ensure nothing was in the new set up.. No problems since..

I know this is a lot of work but that’s what took care of my issue.

p.s - If original to your GT350, save all of your original parts..

Let us know what happens and good luck..

 

Its for a sled pull truck with a 390.

New lines from the pickup to the new fuel pump (new last year) and a new line from the pump to the carb with a inline filter after the pump. I had pulled the pickup from the tank and checked out the tank and it looked fine, no rust or anything in it, or the filter. I think the debris in the car was from me having a blonde moment and not flushing out the new dual feed kit before installing it.

The thing that makes me believe its the carb 100% is the fact that the edelbrock 600 has been a go to no problem carb. I can pull the demon, and put on the eddy and it works perrrrfectly. So it has to be a carb issue.

Thanks for the ideas. I did learn the fuel line tank inspection replacement thing a good while ago, Its way easier to do that than to chase problems that 20.00 in fuel line and a filter could have fixed along with a peak inside the tank.

 

10-4 gottcha.. The only other thing I can think of is - the float and or it's internal moving parts / clearence.. Higher than normal fuel pressure can cause flooding as well ( fuel lines routed by exhaust manifolds or high heat areas that create heat can cause somewhat higher fuel pressure )..

 

I checked to make sure the float wasn't catching on anything when i had it apart, not saying it isn't, just didn't notice it. I will check that again when i tear it apart to check the floats.

I had thought it could be the hot fuel situation, until the last time i had it started and i could still tap the ex. header with my hand and it was still doing it. I did buy more fuel line to route farther away. It literally was only running for 20-30 seconds (just long enough for it to idle since it has no choke) and i walked around to look and could hear it and see the glasses were overrun with fuel.

The float theory, would make sense because it didn't do it the first day or 2 i had it on the truck ( it was dry for over 6 months sitting in the house) so that would have been long enough if they had a prob to soak up the gas.

Hopefully i'll get a chance weds to tear it apart. I havn't had time to do much lately.

 

Got into situation where the carb was flooding and dumping fuel onto the intake manifold, stranded so ended up tapping on the fuel bowl and was able to drive home. Couple days later had the same problem and ended up replacing needles and seats, seems to have solved the problem?

 

funny, i had actually tried the tapping thing. Didn't do anything lol

Planning on tearing into it tomorrow unless somthing comes up

 

I think i got it fixed. New floats and needles/seats. so far float leves are holding. I just put it back on today so I'll see what its like in a few days.

I'm pretty sure the floats were soaking up gas, they were the black foam style floats.


Its a little rich at idle, but i'll have ti tinker with that when i adjust the corners in again.